A. A. Vidotto

GJ 504, a star almost the same age as our Sun, is spinning with remarkable vigor: it completes a full rotation in just 3.4 Earth days, while actively emitting X-rays. For comparison, typical stars of the Sun's age rotate much more slowly, as if they've lost their youthful energy. GJ 504, however, behaves like a figure skater who has received a powerful push and launched into a rapid spin.

Rocky planets orbit dim red stars. Some of them have a year shorter than an Earth day: these worlds are called ultra-short-period planets. Their surfaces are scorching, and their skies are forever bathed in crimson light.